Several components such as those used in land-based and aero gas turbines, steam turbine boilers, and chemical processing equipment operate in severe oxidizing and hot corrosion environments. These components may operate in frequent on-off mode. As a result the components may be exposed to high temperatures and experience thermal cycling between the operating temperatures (relatively high temperatures) and room temperature, which may result in relatively high thermal stresses in the coating and the protective oxide scale.
MCrAl(Y) coatings have been applied to these components via low pressure plasma spray, plasma vacuum spray or high velocity oxy flame processes. Upon exposure to high temperature environments (700° C. to 1200° C.) the aluminum present in the coating proximate to the outer surface reacts with oxygen in the environment, forming an Al2O3 oxide layer, which protects the component from further oxidation. However, during thermal cycling, the high thermal stresses may cause spallation of the Al2O3 coating, which may be accelerated by the presence and formation of mixed oxides including NiO, Cr2O3 and spinels that may form with the Al2O3. As spallation occurs, aluminum in the coating may diffuse towards the surface to replenish the Al2O3 coating. It may be appreciated that the aluminum may diffuse not only towards the surface of the coating, but also into the substrate. Thus, the coating service life may be dependent upon the amount of aluminum present and the potential rate of aluminum consumption.